Method and apparatus for performing buffer status reporting procedure for relaying in wireless communication system

ABSTRACT

A method and apparatus for performing a buffer status reporting (BSR) procedure in a wireless communication system is provided. A relay user equipment (UE) receives data to be relayed from a remote UE via sidelink, triggers a BSR or a sidelink BSR for the data to be relayed, and transmits the BSR or the sidelink BSR to a network.

TECHNICAL FIELD

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for performing a buffer statusreporting (BSR) procedure for relaying in a wireless communicationsystem.

BACKGROUND ART

3rd generation partnership project (3GPP) long-term evolution (LTE) is atechnology for enabling high-speed packet communications. Many schemeshave been proposed for the LTE objective including those that aim toreduce user and provider costs, improve service quality, and expand andimprove coverage and system capacity. The 3GPP LTE requires reduced costper bit, increased service availability, flexible use of a frequencyband, a simple structure, an open interface, and adequate powerconsumption of a terminal as an upper-level requirement.

Recently, there has been a surge of interest in supportingproximity-based services (ProSe). Proximity is determined (“a userequipment (UE) is in proximity of another UE”) when given proximitycriteria are fulfilled. This new interest is motivated by severalfactors driven largely by social networking applications, and thecrushing data demands on cellular spectrum, much of which is localizedtraffic, and the under-utilization of uplink frequency bands. 3GPP istargeting the availability of ProSe in LTE rel-12 to enable LTE become acompetitive broadband communication technology for public safetynetworks, used by first responders. Due to the legacy issues and budgetconstraints, current public safety networks are still mainly based onobsolete 2G technologies while commercial networks are rapidly migratingto LTE. This evolution gap and the desire for enhanced services have ledto global attempts to upgrade existing public safety networks. Comparedto commercial networks, public safety networks have much more stringentservice requirements (e.g., reliability and security) and also requiredirect communication, especially when cellular coverage fails or is notavailable. This essential direct mode feature is currently missing inLTE.

A buffer status reporting (BSR) procedure is used to provide the servingeNodeB (eNB) with information about the amount of data available fortransmission in the uplink (UL) buffers of the UE. As ProSe isintroduced in Rel-12, ProSe BSR may be newly defined.

By using concept of ProSe function, the extension of network coverageusing L3-based UE-to-Network Relay and/or UE-to-UE Relay have beendiscussed. For UE-to-Network Relay and/or UE-to-UE Relay, how to use aBSR for data to be relayed may be required to be defined.

DISCLOSURE OF INVENTION Technical Problem

The present invention provides a method and apparatus for performing abuffer status reporting (BSR) procedure for relaying in a wirelesscommunication system. The present invention provides a method andapparatus for using an uplink (UL) BSR or a sidelink (SL) BSR for userequipment (UE)-to-Network Relay or UE-to-UE Relay.

Solution to Problem

In an aspect, a method for performing, by a relay user equipment (UE), abuffer status reporting (BSR) procedure in a wireless communicationsystem is provided. The method includes receiving data to be relayedfrom a remote UE via sidelink, trigger a BSR or a sidelink BSR for thedata to be relayed, and transmit the BSR or the sidelink BSR to anetwork.

In another aspect, a relay user equipment (UE) in a wirelesscommunication system is provided. The relay UE includes a memory, atransceiver, and a processor coupled to the memory and the transceiver.The processor is configured to control the transceiver to receive datato be relayed from a remote UE via sidelink, trigger a buffer statusreporting (BSR) or a sidelink BSR for the data to be relayed, andcontrol the transceiver to transmit the BSR or the sidelink BSR to anetwork.

Advantageous Effects of Invention

UE-to-Network Relay or UE-to-UE Relay can be performed efficiently.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem.

FIG. 4 shows a block diagram of a control plane protocol stack of an LTEsystem.

FIG. 5 shows an example of a physical channel structure.

FIG. 6 shows a user plane protocol stack for ProSe direct communication.

FIG. 7 shows a control plane protocol stack for ProSe directcommunication.

FIG. 8 shows PC5 interface for ProSe direct discovery.

FIG. 9 shows L2 structure for UL.

FIG. 10 shows L2 structure for SL.

FIG. 11 shows an example of UE-to-Network Relay and UE-to-UE Relay.

FIG. 12 shows a UE-to-Network Relay procedure according to an embodimentof the present invention.

FIG. 13 shows an example of short BSR and truncated BSR MAC CE.

FIG. 14 shows an example of long BSR MAC CE.

FIG. 15 shows an example of SL BSR MAC CE for even N.

FIG. 16 shows an example of SL BSR MAC CE for odd N.

FIG. 17 shows a method for performing, by a relay UE, a BSR procedureaccording to an embodiment of the present invention.

FIG. 18 shows a wireless communication system to implement an embodimentof the present invention.

MODE FOR THE INVENTION

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), anaccess point, etc. One eNB 20 may be deployed per cell.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) and a systemarchitecture evolution (SAE) gateway (S-GW). The MME/S-GW 30 may bepositioned at the end of the network and connected to an externalnetwork. For clarity, MME/S-GW 30 will be referred to herein simply as a“gateway,” but it is understood that this entity includes both the MMEand S-GW.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), packet data network (PDN)gateway (P-GW) and S-GW selection, MME selection for handovers with MMEchange, serving GPRS support node (SGSN) selection for handovers to 2Gor 3G 3GPP access networks, roaming, authentication, bearer managementfunctions including dedicated bearer establishment, support for publicwarning system (PWS) (which includes earthquake and tsunami warningsystem (ETWS) and commercial mobile alert system (CMAS)) messagetransmission. The S-GW host provides assorted functions includingper-user based packet filtering (by e.g., deep packet inspection),lawful interception, UE Internet protocol (IP) address allocation,transport level packet marking in the DL, UL and DL service levelcharging, gating and rate enforcement, DL rate enforcement based onaccess point name aggregate maximum bit rate (APN-AMBR).

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 is connected to the eNB 20 via a Uu interface. The eNBs 20 areconnected to each other via an X2 interface. Neighboring eNBs may have ameshed network structure that has the X2 interface. A plurality of nodesmay be connected between the eNB 20 and the gateway 30 via an S1interface.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC. Referring to FIG. 2, the eNB 20 may perform functions ofselection for gateway 30, routing toward the gateway 30 during a radioresource control (RRC) activation, scheduling and transmitting of pagingmessages, scheduling and transmitting of broadcast channel (BCH)information, dynamic allocation of resources to the UEs 10 in both ULand DL, configuration and provisioning of eNB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE_IDLE state management,ciphering of the user plane, SAE bearer control, and ciphering andintegrity protection of NAS signaling.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem. FIG. 4 shows a block diagram of a control plane protocol stackof an LTE system. Layers of a radio interface protocol between the UEand the E-UTRAN may be classified into a first layer (L1), a secondlayer (L2), and a third layer (L3) based on the lower three layers ofthe open system interconnection (OSI) model that is well-known in thecommunication system.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Databetween the MAC layer and the PHY layer is transferred through thetransport channel. Between different PHY layers, i.e. between a PHYlayer of a transmission side and a PHY layer of a reception side, datais transferred via the physical channel.

A MAC layer, a radio link control (RLC) layer, and a packet dataconvergence protocol (PDCP) layer belong to the L2. The MAC layerprovides services to the RLC layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides data transferservices on logical channels. The RLC layer supports the transmission ofdata with reliability. Meanwhile, a function of the RLC layer may beimplemented with a functional block inside the MAC layer. In this case,the RLC layer may not exist. The PDCP layer provides a function ofheader compression function that reduces unnecessary control informationsuch that data being transmitted by employing IP packets, such as IPv4or IPv6, can be efficiently transmitted over a radio interface that hasa relatively small bandwidth.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer controls logical channels, transportchannels, and physical channels in relation to the configuration,reconfiguration, and release of radio bearers (RBs). The RB signifies aservice provided the L2 for data transmission between the UE andE-UTRAN.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid ARQ (HARQ). The PDCP layer (terminatedin the eNB on the network side) may perform the user plane functionssuch as header compression, integrity protection, and ciphering.

Referring to FIG. 4, the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The RRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

FIG. 5 shows an example of a physical channel structure. A physicalchannel transfers signaling and data between PHY layer of the UE and eNBwith a radio resource. A physical channel consists of a plurality ofsubframes in time domain and a plurality of subcarriers in frequencydomain. One subframe, which is 1 ms, consists of a plurality of symbolsin the time domain. Specific symbol(s) of the subframe, such as thefirst symbol of the subframe, may be used for a physical downlinkcontrol channel (PDCCH). The PDCCH carries dynamic allocated resources,such as a physical resource block (PRB) and modulation and coding scheme(MCS).

A DL transport channel includes a broadcast channel (BCH) used fortransmitting system information, a paging channel (PCH) used for paginga UE, a downlink shared channel (DL-SCH) used for transmitting usertraffic or control signals, a multicast channel (MCH) used for multicastor broadcast service transmission. The DL-SCH supports HARQ, dynamiclink adaptation by varying the modulation, coding and transmit power,and both dynamic and semi-static resource allocation. The DL-SCH alsomay enable broadcast in the entire cell and the use of beamforming.

A UL transport channel includes a random access channel (RACH) normallyused for initial access to a cell, a uplink shared channel (UL-SCH) fortransmitting user traffic or control signals, etc. The UL-SCH supportsHARQ and dynamic link adaptation by varying the transmit power andpotentially modulation and coding. The UL-SCH also may enable the use ofbeamforming.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting multimedia broadcast multicast services(MBMS) control information from the network to a UE. The DCCH is apoint-to-point bi-directional channel used by UEs having an RRCconnection that transmits dedicated control information between a UE andthe network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink The MTCH is apoint-to-multipoint downlink channel for transmitting traffic data fromthe network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. The RRC state may be dividedinto two different states such as an RRC idle state (RRC_IDLE) and anRRC connected state (RRC_CONNECTED). In RRC_IDLE, the UE may receivebroadcasts of system information and paging information while the UEspecifies a discontinuous reception (DRX) configured by NAS, and the UEhas been allocated an identification (ID) which uniquely identifies theUE in a tracking area and may perform public land mobile network (PLMN)selection and cell re-selection. Also, in RRC_IDLE, no RRC context isstored in the eNB.

In RRC_CONNECTED, the UE has an E-UTRAN RRC connection and a context inthe E-UTRAN, such that transmitting and/or receiving data to/from theeNB becomes possible. Also, the UE can report channel qualityinformation and feedback information to the eNB. In RRC_CONNECTED, theE-UTRAN knows the cell to which the UE belongs. Therefore, the networkcan transmit and/or receive data to/from UE, the network can controlmobility (handover and inter-radio access technologies (RAT) cell changeorder to GSM EDGE radio access network (GERAN) with network assistedcell change (NACC)) of the UE, and the network can perform cellmeasurements for a neighboring cell.

In RRC_IDLE, the UE specifies the paging DRX cycle. Specifically, the UEmonitors a paging signal at a specific paging occasion of every UEspecific paging DRX cycle. The paging occasion is a time interval duringwhich a paging signal is transmitted. The UE has its own pagingoccasion. A paging message is transmitted over all cells belonging tothe same tracking area. If the UE moves from one tracking area (TA) toanother TA, the UE will send a tracking area update (TAU) message to thenetwork to update its location.

Proximity-based services (ProSe) are described. “ProSe” may be usedmixed with “D2D”. ProSe direct communication means a communicationbetween two or more UEs in proximity that are ProSe-enabled, by means ofuser plane transmission using E-UTRA technology via a path nottraversing any network node. ProSe-enabled UE means a UE that supportsProSe requirements and associated procedures. Unless explicitly statedotherwise, a ProSe-enabled UE refers both to a non-public safety UE anda public safety UE. ProSe-enabled public safety UE means a ProSe-enabledUE that also supports ProSe procedures and capabilities specific topublic safety. ProSe-enabled non-public safety UE means a UE thatsupports ProSe procedures and but not capabilities specific to publicsafety. ProSe direct discovery means a procedure employed by aProSe-enabled UE to discover other ProSe-enabled UEs in its vicinity byusing only the capabilities of the two UEs with 3GPP LTE rel-12technology. EPC-level ProSe discovery means a process by which the EPCdetermines the proximity of two ProSe-enabled UEs and informs them oftheir proximity. ProSe UE identity (ID) is a unique identity allocatedby evolved packet system (EPS) which identifies the ProSe enabled UE.ProSe application ID is an identity identifying application relatedinformation for the ProSe enabled UE.

Sidelink (SL) is UE to UE interface for ProSe direct communication andProSe direct discovery. Sidelink comprises ProSe direct discovery andProSe direct communication between UEs. Sidelink uses UL resources andphysical channel structure similar to UL transmissions. Sidelinktransmission uses the same basic transmission scheme as the ULtransmission scheme. However, sidelink is limited to single clustertransmissions for all the sidelink physical channels. Further, sidelinkuses a 1 symbol gap at the end of each sidelink sub-frame.

For mapping between sidelink transport channels and sidelink physicalchannels, a sidelink discovery channel (SL-DCH) may be mapped to aphysical sidelink discovery channel (PSDCH), which carries ProSe directdiscovery message from the UE. The SL-DCH is characterized by:

fixed size, pre-defined format periodic broadcast transmission;

support for both UE autonomous resource selection and scheduled resourceallocation by eNB;

collision risk due to support of UE autonomous resource selection; nocollision when UE is allocated dedicated resources by the eNB.

Further, a sidelink shared channel (SL-SCH) may be mapped to a physicalsidelink shared channel (PSSCH), which carries data from a UE for ProSedirect communication. The SL-SCH is characterized by:

support for broadcast transmission;

support for both UE autonomous resource selection and scheduled resourceallocation by eNB;

collision risk due to support of UE autonomous resource selection; nocollision when UE is allocated dedicated resources by the eNB;

support for HARQ combining, but no support for HARQ feedback;

support for dynamic link adaptation by varying the transmit power,modulation and coding.

Further, a sidelink broadcast channel (SL-BCH) may be mapped to aphysical sidelink broadcast channel (PSBCH), which carries system andsynchronization related information transmitted from the UE. The SL-BCHis characterized by pre-defined transport format.

A physical sidelink control channel (PSCCH) carries control from a UEfor ProSe direct communication. The PSCCH is mapped to the sidelinkcontrol resources. The PSCCH indicates resource and other transmissionparameters used by a UE for PSSCH.

For mapping between sidelink logical channels and sidelink transportchannels for ProSe direct communication, a sidelink broadcast controlchannel (SBCCH) may be mapped to the SL-BCH. The SBCCH is a sidelinkchannel for broadcasting sidelink system information from one UE toother UE(s). This channel is used only by ProSe direct communicationcapable UEs. Further, a sidelink traffic channel (STCH) may be mapped tothe SL-SCH. The STCH is a point-to-multipoint channel, for transfer ofuser information from one UE to other UEs. This channel is used only byProSe direct communication capable UEs.

ProSe direct communication is a mode of communication whereby UEs cancommunicate with each other directly over the PC5 interface. Thiscommunication mode is supported when the UE is served by E-UTRAN andwhen the UE is outside of E-UTRA coverage. Only those UEs authorized tobe used for public safety operation can perform ProSe directcommunication.

In order to perform synchronization for out of coverage operation, UE(s)may act as a synchronization source by transmitting SBCCH and asynchronization signal. SBCCH carries the most essential systeminformation needed to receive other ProSe channels and signals. SBCCHalong with synchronization signal is transmitted with a fixedperiodicity of 40 ms. When the UE is in network coverage, the contentsof SBCCH are derived from the parameters signaled by the eNB. When theUE is out of coverage, if the UE selects another UE as a synchronizationreference, then the content of SBCCH is derived from the received SBCCH.Otherwise, UE uses pre-configured parameters. System information block(SIB) 18 provides the resource information for synchronization signaland SBCCH transmission. There are two pre-configured subframes every 40ms for out of coverage operation. UE receives synchronization signal andSBCCH in one subframe and transmit synchronization signal and SBCCH onanother subframe if UE becomes synchronization source.

UE performs Prose direct communication on subframes defined over theduration of sidelink control (SC) period. The SC period is the periodover which resources allocated in a cell for sidelink control andsidelink data transmissions occur. Within the SC period, the UE sends asidelink control followed by sidelink data. Sidelink control indicates alayer 1 ID and characteristics of the transmissions (e.g. MCS, locationof the resource(s) over the duration of SC period, timing alignment).

The UE performs transmission and reception of Uu and PC5 with thefollowing decreasing priority order:

Uu transmission/reception (highest priority)

PC5 ProSe direct communication transmission/reception

PC5 ProSe direct discovery transmission/reception (lowest priority)

FIG. 6 shows a user plane protocol stack for ProSe direct communication.Referring to FIG. 6, PDCP, RLC and MAC sublayers (terminate at the otherUE) perform the functions listed for the user plane. The AS protocolstack in the PC5-U interface consists of PDCP, RLC, MAC and PHY.

There is no HARQ feedback for ProSe direct communication. RLCunacknowledged mode (UM) is used for ProSe direct communication. Areceiving UE needs to maintain at least one RLC UM entity pertransmitting peer UE. A receiving RLC UM entity used for ProSe directcommunication does not need to be configured prior to reception of thefirst RLC unacknowledged mode data (UMD) protocol data unit (PDU).Robust header compression (ROHC) unidirectional mode is used for headercompression in PDCP for ProSe direct communication.

A UE may establish multiple logical channels. Logical channel ID (LCID)included within the MAC subheader uniquely identifies a logical channelwithin the scope of one source Layer-2 ID and ProSe layer-2 group IDcombination. Parameters for logical channel prioritization are notconfigured.

FIG. 7 shows a control plane protocol stack for ProSe directcommunication. Referring to FIG. 7, PDCP, the AS protocol stack forSBCCH in the PC5-C interface consists of RRC, RLC, MAC and PHY. A UEdoes not establish and maintain a logical connection to receiving UEsprior to a ProSe direct communication.

For ProSe direct communication, the UE supporting ProSe directcommunication can operate in two modes for resource allocation, whichinclude Mode 1 (scheduled resource allocation) and Mode 2 (UE autonomousresource selection). In Mode 1, the UE needs to be RRC_CONNECTED inorder to transmit data. The UE requests transmission resources from theeNB. The eNB schedules transmission resources for transmission ofsidelink control and data. The UE sends a scheduling request (dedicatedscheduling request (D-SR) or random access) to the eNB followed by aProSe buffer status report (BSR). Based on the ProSe BSR, the eNB candetermine that the UE has data for a ProSe direct communicationtransmission and estimate the resources needed for transmission. The eNBcan schedule transmission resources for ProSe direct communication usingconfigured sidelink radio network temporary identifier (SL-RNTI). InMode 2, a UE on its own selects resources from resource pools andperforms transport format selection to transmit sidelink control anddata.

A UE in RRC_CONNECTED may send a ProSe UE Information indication to eNBwhen UE becomes interested in ProSe Direct Communication. In responseeNB may configure the UE with a SL-RNTI.

A UE is considered in-coverage for ProSe direct communication wheneverit detects a cell on a public safety ProSe carrier. If the UE is out ofcoverage for ProSe direction communication, it can only use Mode 2. Ifthe UE is in coverage for ProSe direct communication, it may use Mode 1or Mode 2 as per eNB configuration. If the UE is in coverage for ProSedirect communication, it shall use only Mode 1 unless one of theexceptional cases occurs. When an exceptional case occurs, the UE isallowed to use Mode 2 temporarily even though it was configured to useMode 1. Resource pool to be used during exceptional case may be providedby eNB.

A UE that is camped or connected on one carrier frequency but interestedin ProSe direct communication operation on another carrier frequency(i.e. public safety ProSe carrier) shall attempt to find cells on thepublic safety ProSe carrier. An RRC_IDLE UE camped on a cell in anothercarrier frequency, but in the coverage area of an E-UTRA cell on publicsafety ProSe carrier, may consider the public safety ProSe carrier to behighest priority, and reselects to the cell on the public safety ProSecarrier. UE may consider a frequency (non-public safety ProSe carrier)to be highest priority if it can perform ProSe direct communication onlywhile camping on the frequency.

An RRC_CONNECTED UE served by a cell in another carrier frequency maysend a ProSe UE Information indication to its serving cell when it wantsto perform ProSe direct communication. The indication contains theintended public safety ProSe carrier. The serving cell indicates withthe presence of SIB 18 whether the UE is allowed to send the ProSe UEInformation indication. The serving cell may configure an interfrequencyradio resource management (RRM) measurement on the public safety ProSecarrier. Once the UE enters coverage of a cell on the public safetyProSe carrier, based on measurement report, the eNB performsinter-frequency mobility to the public safety ProSe carrier. Ifinter-frequency mobility is not performed by the serving cell, or if itfails, the UE may still perform ProSe direct communication using Mode 2from the resource pools, if any, broadcasted by the detected E-UTRA cellon the public safety ProSe carrier.

If the UE does not detect an E-UTRA cell on the public safety ProSecarrier, the UE can use public safety ProSe carrier resourcespreconfigured in the universal integrated circuit card (UICC) or mobileequipment (ME) for out of coverage ProSe direct communication. If the UEdetects an E-UTRA cell on the public safety ProSe carrier, the UE stopsusing resources preconfigured in the UICC or ME. UE may use Mode 2 fromthe resource pools, if any, broadcasted by the detected E-UTRA cell onthe public safety ProSe carrier. For Rel-12, all ProSe communication(for a UE) is performed on a single preconfigured public safety ProSecarrier, which is valid in the operating region. Higher layers checkvalidity of the public safety ProSe carrier in the operating region.

The cell on the public safety ProSe carrier may provide a transmissionresource pool for Mode 2 in SIB 18. UEs that are authorized for Prosedirect communication may use these resources for ProSe directcommunication in RRC IDLE in the cell in the same carrier (i.e. publicsafety ProSe carrier). UEs that are authorized for ProSe directcommunication may use these resources for ProSe direct communication inRRC_IDLE in the cell on the same carrier (i.e. public safety ProSecarrier). UEs that are authorized for ProSe direct communication may usethese resources for ProSe direct communication in RRC IDLE or RRCCONNECTED in a cell on another carrier.

Alternatively, the cell on the public safety ProSe carrier may indicatein SIB 18 that it supports ProSe direct communication but does notprovide transmission resources. UEs need to enter RRC_CONNECTED toperform ProSe direct communication transmission. In this case, the cellon the public safety ProSe carrier may provide, in broadcast signaling,an exceptional transmission resource pool for Mode 2, to be used by theUE in exceptional cases. A UE in RRC_CONNECTED that is authorized toperform ProSe direct communication transmission indicates to the servingeNB that it wants to perform ProSe direct communication transmissions.The eNB validates whether the UE is authorized for ProSe directcommunication transmission using the UE context received from MME. TheeNB may configure a UE by dedicated signaling with a transmissionresource pool for Mode 2. That may be used without constraints while theUE is RRC_CONNECTED. Alternatively, the eNB may configure a UE to usethe exceptional transmission resource pool for Mode 2 which the UE isallowed to use only in exceptional cases, and rely on scheduled resourceallocation otherwise.

The resource pools for sidelink control when the UE is out of coverageare preconfigured for reception and transmission. The resource pools forsidelink control when the UE is in coverage for ProSe directcommunication are configured as below. The resource pool used forreception is configured by the eNB via RRC, in broadcast signaling. Theresource pool used for transmission is configured by the eNB via RRC, indedicated or broadcast signaling, if Mode 2 is used. The resource poolused for transmission is configured by the eNB via RRC, in dedicatedsignaling, if Mode 1 is used. The eNB schedules the specific resource(s)for sidelink control transmission within the configured reception pool.In order to perform communication even when some UEs are in-coverage andsome UEs are out of coverage, all UEs (i.e. both in and out of coverage)should be configured with reception resource pools for sidelink controlwhich are the union of the resource pools used for transmission ofsidelink control in the serving cell and neighbor cells and transmissionof sidelink control for out of coverage.

The resource pools for data when the UE is out of coverage for ProSedirect communication are pre-configured for reception and transmission.The resource pools for data when the UE is in coverage for ProSe directcommunication are configured by the eNB via RRC, in dedicated orbroadcast signaling, if Mode 2 is used, for reception and transmission.There is no resource pool for transmission if Mode 1 is used.

ProSe direct discovery is defined as the procedure used by the UEsupporting ProSe direct discovery to discover other UE(s) in itsproximity, using E-UTRA direct radio signals via PC5. ProSe directdiscovery is supported only when the UE is served by E-UTRAN. Upperlayer handles authorization for announcement and monitoring of discoverymessage. Content of discovery message is transparent to AS and nodistinction in AS is made for ProSe direct discovery models and types ofProSe direct discovery. The ProSe protocol ensures that only validdiscovery messages are delivered to AS for announcement.

The UE can participate in announcing and monitoring of discovery messagein both

RRC_IDLE and RRC_CONNECTED states as per eNB configuration. The UEannounces and monitors its discovery message subject to the half-duplexconstraint. The UE that participates in announcing and monitoring ofdiscovery messages maintains the current coordinated universal timecoordinated (UTC) time. The UE that participates in announcing transmitsthe discovery message which is generated by the ProSe protocol takinginto account the UTC time upon transmission of the discovery message. Inthe monitoring UE, the ProSe protocol provides the message to beverified together with the UTC time upon reception of the message to theProSe function.

In order to perform synchronization, UE(s) participating in announcingof discovery messages may act as a synchronization source bytransmitting a synchronization signal based on the resource informationfor synchronization signals provided in SIB19.

There are three range classes. Upper layer authorization providesapplicable range class of the UE. Maximum allowed transmission power foreach range class is signaled in SIB 19. UE uses the applicable maximumallowed transmission power corresponding to its authorized range class.This puts an upper limit on the determined transmit power based on openloop power control parameters.

FIG. 8 shows PC5 interface for ProSe direct discovery. Referring to FIG.8, UE A and UE B perform ProSe direct discovery using ProSe protocol viaPC5-D. Radio protocol stack (AS) for ProSe direct discovery consists ofonly MAC and PHY. The AS layer performs function of interfaces withupper layer (ProSe Protocol). The MAC layer receives the discoverymessage from the upper layer (ProSe Protocol). The IP layer is not usedfor transmitting the discovery message. The AS layer also performsfunction of scheduling. The MAC layer determines the radio resource tobe used for announcing the discovery message received from upper layer.The AS layer also performs function of discovery PDU generation. The MAClayer builds the MAC PDU carrying the discovery message and sends theMAC PDU to the physical layer for transmission in the determined radioresource. No MAC header is added.

There are two types of resource allocation for discovery messageannouncement, which include Type 1 (UE autonomous resource selection)and Type 2 (scheduled resource allocation). Type 1 is a resourceallocation procedure where resources for announcing of discovery messageare allocated on a non UE specific basis. In Type 1, the eNB providesthe UE(s) with the resource pool configuration used for announcing ofdiscovery message. The configuration may be signaled in broadcast ordedicated signaling. The UE autonomously selects radio resource(s) fromthe indicated resource pool and announce discovery message. The UE canannounce discovery message on a randomly selected discovery resourceduring each discovery period. Type 2 is a resource allocation procedurewhere resources for announcing of discovery message are allocated on perUE specific basis. In Type 2, the UE in RRC_CONNECTED may requestresource(s) for announcing of discovery message from the eNB via RRC.The eNB assigns resource(s) via RRC. The resources are allocated withinthe resource pool that is configured in UEs for monitoring.

For UEs in RRC_IDLE, the eNB may provide a resource pool for Type 1based discovery message announcement in SIB 19. UEs that are authorizedfor Prose direct discovery use these resources for announcing discoverymessage in RRC_IDLE. Alternatively, the eNB may indicate in SIB 19 thatit supports ProSe direct discovery but does not provide resources fordiscovery message announcement. UEs need to enter RRC_CONNECTED in orderto request resources for discovery message announcement.

For UEs in RRC_CONNECTED, a UE authorized to perform ProSe directdiscovery announcement indicates to the eNB that it wants to performProSe direct discovery announcement. The eNB validates whether the UE isauthorized for ProSe direct discovery announcement using the UE contextreceived from MME. The eNB may configure the UE with resource pool forType 1 for discovery message announcement via dedicated signaling. TheeNB may configure resource pool along with dedicated resource in theform of time and frequency indices for discovery message announcementvia dedicated RRC signaling. The dedicated resources allocated by theeNB are valid until the eNB re-configures the resource(s) by RRCsignaling, or the UE enters RRC_IDLE.

Authorized receiving UEs in RRC_IDLE and RRC_CONNECTED monitor resourcepools used for Type 1 and resource pools for Type 2. The eNB providesthe resource pool configuration used for discovery message monitoring inSIB 19. The SIB 19 may contain detailed ProSe direct discoveryconfiguration used for announcing in neighbor cells of intra-frequencyas well.

Synchronous and asynchronous deployments are supported. Discoveryresources can be overlapping or non-overlapping across cells.

A UE, if authorized by the network, can announce discovery message onlyon serving cell. The UE can monitor discovery resources in the same aswell as other frequencies than the serving cell, in same or differentPLMNs. The serving cell may provide in SIB 19 a list of frequenciesalong with PLMN ID on which the UE may aim to monitor discovery message.The serving cell does not provide detailed ProSe discovery configurationfor other carrier frequencies. The UE shall read SIB 19 and otherrelevant SIBs on other carriers if it wants to perform discovery messagemonitoring on those carriers. Obtaining ProSe direct discoveryconfiguration by reading SIB 19 (and other SIBs) of an inter-frequencyand/or inter-PLMN cell shall not affect the UE's Uu reception on theserving cell(s). The UE performs intra-frequency ProSe direct discoveryannouncement in subframes in which a ProSe direct discovery resourcepool is configured and the UE is not expected to perform uplink Uutransmission. In this case, the UE shall not create autonomous gaps.Intra-frequency, inter-frequency and inter-PLMN ProSe direct discoverymonitoring shall not affect Uu reception. The UE uses DRX occasions inRRC_IDLE and RRC_CONNECTED or second RX chain if it is available, forintra-frequency, inter-frequency and inter-PLMN discovery messagemonitoring. The UE shall not create autonomous gaps. An RRC_CONNECTED UEsends ProSe UE Information indication to the serving cell if it isinterested or no longer interested in intra-frequency, inter-frequencyor inter-PLMN discovery message monitoring.

FIG. 9 shows L2 structure for UL. FIG. 10 shows L2 structure for SL.Layer 2 is split into the sublayers of MAC, RLC and PDCP. Referring toFIG. 9, in UL, only one transport block is generated per transmissiontime interval (TTI) in the absence of spatial multiplexing. Referring toFIG. 10, in SL, only one transport block is generated per TTI. And inSL, transmission (TX) entity and reception (RX) entity are configuredseparately.

BSR is needed to provide support for quality of service (QoS)-awarepacket scheduling. In E-UTRAN, BSR refers to the data that is bufferedin for a group of logical channel (LCG) in the UE. BSR is transmittedusing MAC signaling. The UL BSR procedure is used to provide the servingeNB with information about the amount of UL data available fortransmission in the UL buffers associated with the MAC entity. The SLBSR procedure is used to provide the serving eNB with information aboutthe amount of SL data available for transmission in the SL buffers ofthe MAC entity.

FIG. 11 shows an example of UE-to-Network Relay and UE-to-UE Relay.Referring to FIG. 11, UE1 performs as a ProSe UE-to-Network Relay UE(hereinafter, relay UE). Relay UE is a UE that provides functionality tosupport connectivity to unicast services for remote UE(s). UE2 performsas a remote UE. Remote UE is a ProSe-enabled public safety UE thatcommunicates with a PDN via a ProSe UE-to-Network Relay. That is, UE1,i.e. relay UE, receives from control signal/data from UE2, i.e. remoteUE, which is required to be relayed to the network or another UE, i.e.UE3. If the control signal/data is relayed to the network, it mayconsist of UE-to-Network Relay. If the control signal/data is relayed toUE3, it may consist of UE-to-UE Relay.

From the perspective of the remote UE, there may be some data whichneeds to be relayed to the network among one-to-many communication.However, the current MAC procedure, specifically BSR procedure, does notsupport UE-to-Network Relay and/or UE-to-UE Relay.

In order to solve the problem described above, a method for performing aBSR procedure for relay according to an embodiment of the presentinvention is proposed below. In the description below, UE-to-NetworkRelay may be mainly focused for the convenience, however, the presentinvention is not limited to thereto. The present invention describedbelow may be applied to UE-to-UE Relay as well. Relay may refer toUE-to-UE relay as well as UE-to-Network Relay in the description below.Further, it is assumed that UE1 (receiver UE) is relay UE that canprovide the relay service and UE2 (transmitter UE) is a remote UE thatwants to get the relay service. Further, there may be two types of relayservices, one of which is a relay service for 1:M data transmitted byremote UE and the other is a relay service for 1:1 data transmitted byremote UE.

For UE-to-Network Relay, if relayed data is delivered from the remote UEtowards the network, the data is delivered from PC5 interface (in SL) toUu interface (in UL) in the relay UE. According to an embodiment of thepresent invention, the UL BSR or the SL BSR may be used to inform theserving eNB about the amount of data available for UL transmission ofrelayed data. That is, for reflecting a buffer status of relayed data,the UL BSR or SL BSR may be used. In this case, a LCG may be dedicatedto relay in the UL BSR or SL BSR.

Further, according to another embodiment of the present invention, thebuffer size reflecting relayed data in the UL BSR or SL BSR may includenot only UL data in a TX L2 entity over Uu interface, but also SL datain a RX L2 entity over PC5 interface (i.e. relayed data). If the UL BSRis used for relayed data, data available for relay transmission in a RXL2 entity over PC5 interface may trigger the UL BSR. If the SL BSR isused for relayed data, data available for relay transmission in a TX L2entity over Uu interface may trigger the SL BSR. All triggered UL/SLBSRs reflecting relayed data from the ProSe Source for the ProSeDestination may be cancelled when the UL/SL BSR reflecting relayed datafrom the ProSe Source for the ProSe Destination is included in a MAC PDUfor transmission.

Further, according to another embodiment of the present invention, whenthe UL BSR reflects relayed data for a group of which priority ischanged due to emergency situation, the MAC entity of the relay UE mayprioritize the UL BSR over the other BSRs in logical channelprioritization procedure. When the SL BSR reflects relayed data for agroup of which priority is changed due to emergency situation, the MACentity of the relay UE may prioritize the SL BSR over the other SL BSRsin logical channel prioritization procedure, or may prioritize the SLBSR over BSRs and the other SL BSRs in logical channel prioritizationprocedure.

FIG. 12 shows a UE-to-Network Relay procedure according to an embodimentof the present invention.

In step S100, if the UE1 can support relay of data in a group, the UE1transmits a relay request to the eNB. The relay request may include atleast one of source ID, destination ID, QoS related to services in thegroup, or any priority related to mission critical push-to-talk (MCPTT).

In step S110, the eNB transmits a relay configuration to the UE1 toconfigure the UE1 with a data radio bearer which is only used to relaydata. Upon receiving the relay configuration, the UE1 may perform as therelay UE in UE-to-Network Relay. Relayed data for differentsources/destinations may be carried via different radio bearers. Thatis, a radio bearer for relaying data may be configured for each sourceID, each destination ID, or a combination of source ID and destinationID. Further, via the relay configuration, the eNB may inform the UE1which radio bearer is used to relay data between another UE and the eNBfor a source ID and a destination ID. The eNB may inform the UE1 ofmapping relationship between a LCID and a combination of a source ID anda destination ID, mapping relationship between a LCID and a source ID,or mapping relationship between a LCID and a destination ID.

In step S120, the UE1 transmits a relay activation to the UE2 toindicate that the UE1 is ready to relay data transmitted from the UE2.The relay activation may be transmitted via SL-BCH.

If the UE2 detects that there is a relay UE (e.g. the UE1) nearby byreceiving the relay activation, in step S130, the UE2 transmits userdata in sidelink to the UE1. The UE2 may indicate to a relay UE (e.g.the UE1) whether the user data needs to be relayed via SL-BCH, sidelinkcontrol information (SCI), or SL-SCH. SL-BCH may be used to indicate toa relay UE that all user data received for a certain combination ofsource ID and destination ID should be relayed. SCI may be used toindicate to a relay UE that all user data received in the correspondingSC period should be relayed. As a result, the UE1 may determine whetherto relay the user data in every SC period. MAC sub-header or MAC controlelement (CE) included in a MAC PDU on SL-SCH may be used to indicate toa relay UE that the MAC PDU should be relayed. As a result, the UE1 maydetermine whether to relay the user data by every MAC PDU.

Upon receiving the user data from the UE2, the UE1 receives RLC/PDCPservice data units (SDUs) from the UE2 in sidelink and stores in RX L2buffer of RX RLC/PDCP entities for sidelink For relaying L2 SDU, e.g.from PC5 interface to Uu interface (i.e. UE-to-Network Relay) or fromone PC5 interface to another PC5 interface (i.e. UE-to-UE Relay), L2SDUs in RX L2 entity in sidelink are transferred to L2 SDUs in TX L2entity in uplink (i.e. UE-to-Network Relay) or in sidelink (i.e.UE-to-UE Relay). For UE-to-Network Relay, it is likely that PDCP SDUs inTX PDCP entity in sidelink are delivered to PDCP SDUs in TX PDCP entityin uplink The RX PDCP entity over PC5 interface delivers PDCP SDUs to TXPDCP entity over Uu interface either out of sequence or in sequence.Then, those PDCP SDUs are processed in TX PDCP/RLC entities.

In step S140, the UE1 checks UE buffer for relaying the user data andtriggers BSR (i.e. UL BSR) or SL BSR for data to be relayed. That is, inorder for the UE1 to relay the user data received from the eNB2 insidelink to the eNB in uplink, the BSR or the SL BSR may provide theserving eNB with information about the amount of data available forrelaying the user data to be relayed.

(1) BSR may reflect the user data to be relayed. That is, BSR mayprovide the serving eNB with information about the amount of dataavailable for relaying the user data to be relayed. In this case, an LCGmay be dedicated to relaying. The eNB may configure which LCG isdedicated to relaying. The BSR may indicate which LCG in the BSRreflects the amount of data available for relaying the user data to berelayed. The BSR may indicates whether or not the BSR reflects theamount of data available for relaying the user data received from theremote UE.

If the UE1 performs relaying, the UE1 may perform different independentBSR procedures for different sources, for different destinations, or fordifferent combinations of source and destination, when the UE1 relaysthe user data from those source UEs to those destination UEs. Namely,the UE1 may perform a BSR procedure per source ID, per destination ID,or per combination of source ID and destination ID. For example,different timers related to the BSR may be configured for each BSRprocedure. Further, cancelling triggered BSRs may be performedindependently for each BSR procedure.

The buffer size field included in the BSR reflecting the relayed datamay identify the total amount of data available across all logicalchannels of a logical channel group for a source ID, a destination ID,or a combination of a source ID and a destination ID after all MAC PDUsfor the TTI have been built. The buffer size field included in the BSRreflecting the relayed data may include all data that is available fortransmission not only in the TX RLC/PDCP entities over Uu interface butalso in the RX RLC/PDCP entities over PC5 interface.

When the BSR reflects the relayed data for a group of which priority ischanged due to emergency situation, the MAC entity of the relay UE mayprioritize the BSR over the other BSRs in logical channel prioritizationprocedure.

(2) SL BSR may reflect the user data to be relayed. That is, the SL BSRmay provide the serving eNB with information about the amount of dataavailable for relaying the user data to be relayed. In this case, an LCGmay be dedicated to relaying. The eNB may configure which LCG isdedicated to relaying. The SL BSR may indicate which LCG in the SL BSRreflects the amount of data available for relaying the user data to berelayed. The SL BSR indicates which group index in the SL BSR reflectsthe amount of data available for relaying the user data to be relayed.The SL BSR may indicate whether or not the SL BSR reflects the amount ofdata available for relaying the user data to be relayed.

If the UE1 performs relaying, the UE1 may perform different independentSL BSR procedures for different sources, for different destinations, orfor different combinations of source and destination, when the UE1relays the user data from those source UEs to those destination UEs.Namely, the UE1 may perform a SL BSR procedure per source ID, perdestination ID, or per combination of source ID and destination ID. Forexample, different timers related to the SL BSR may be configured foreach SL BSR procedure. Further, cancelling triggered SL BSRs may beperformed independently for each SL BSR procedure.

The buffer size field included in the SL BSR reflecting the relayed datamay identify the total amount of data available across all logicalchannels of a logical channel group for a source ID, a destination ID,or a combination of a source ID and a destination ID after all MAC PDUsfor the TTI have been built. The buffer size field included in the SLBSR reflecting the relayed data may include all data that is availablefor transmission not only in the TX RLC/PDCP entities over Uu interfacebut also in the RX RLC/PDCP entities over PC5 interface.

When the SL BSR reflects the relayed data for a group of which priorityis changed due to emergency situation, the MAC entity of the relay UEmay prioritize the SL BSR over the other SL BSRs in logical channelprioritization procedure, or may prioritize the SL BSR over BSRs and theother SL BSRs in logical channel prioritization procedure.

In step S150, a scheduling request (SR) may be triggered in a BSRprocedure or SL BSR procedure, and may transmit to the eNB. If the eNBconfigures PUCCH resources dedicated to relaying, the SR triggered dueto relaying may be carried on the PUCCH resource dedicated to relaying.Otherwise, the SR may be carried via the same PUCCH resources or viarandom access procedure.

In step S160, the UE1 receives a UL grant from the eNB. The UE1 maymonitor a RNTI dedicated to relaying and then receive the UL grantdedicated to relaying. The RNTI may be dedicated to relaying, a ProSeSource, a ProSe Destination, or a combination of a ProSe Source and aProSe Destination.

In step S170, the UE1 transmits the triggered BSR or the triggered SLBSR.

In step S180, the eNB transmits a relay grant to the UE1.

In step S190, the UE1 transmits the user data to be relayed to the eNB.

When the BSR is used to reflect the user data to be relayed, the BSRprocedure may be performed as follows. The BSR procedure is used toprovide the serving eNB with information about the amount of dataavailable for transmission in the UL buffers associated with the MACentity. The amount of data includes data to be relayed from another UEto the serving eNB. RRC controls BSR reporting by configuring the threetimers periodicBSR-Timer, retxBSR-Timer andlogicalChannelSR-ProhibitTimer and by, for each logical channel,optionally signalling logicalChannelGroup which allocates the logicalchannel to an LCG. For the BSR procedure, the MAC entity shall considerall radio bearers which are not suspended and may consider radio bearerswhich are suspended.

A BSR shall be triggered if any of the following events occur:

UL data, for a logical channel which belongs to a LCG, becomes availablefor transmission in the RLC entity or in the PDCP entity and either thedata belongs to a logical channel with higher priority than thepriorities of the logical channels which belong to any LCG and for whichdata is already available for transmission, or there is no dataavailable for transmission for any of the logical channels which belongto a LCG, in which case the BSR is referred below to as “Regular BSR”;

UL resources are allocated and number of padding bits is equal to orlarger than the size of the BSR MAC CE plus its subheader, in which casethe BSR is referred below to as “Padding BSR”;

retxBSR-Timer expires and the MAC entity has data available fortransmission for any of the logical channels which belong to a LCG, inwhich case the BSR is referred below to as “Regular BSR”;

periodicBSR-Timer expires, in which case the BSR is referred below to as“Periodic BSR”.

if the MAC entity is configured for relay, SL data received in sidelink,for a sidelink logical channel of a ProSe Source, a ProSe Destination,or a combination of a ProSe Source and a ProSe Destination, becomesavailable for relay transmission in the receiving RLC entity over PC5 orin the receiving PDCP entity over PC5 and there is currently no dataavailable for transmission for any of the sidelink logical channelsbelonging to the same ProSe Source, the same ProSe Destination, or thesame combination of a ProSe Source and a ProSe Destination, in whichcase the Sidelink BSR is referred below to as “Regular Sidelink BSR”;

For Regular BSR:

1>if the BSR is triggered due to data becoming available fortransmission for a logical channel for whichlogicalChannelSR-ProhibitTimer is configured by upper layers:

2>if not running, start the logicalChannelSR-ProhibitTimer;

1>else:

2>if running, stop the logicalChannelSR-ProhibitTimer.

For Regular and Periodic BSR:

1>if more than one LCG has data available for transmission in the TTIwhere the BSR is transmitted: report Long BSR;

1>else report Short BSR.

For Padding BSR:

1>if the number of padding bits is equal to or larger than the size ofthe Short BSR plus its subheader but smaller than the size of the LongBSR plus its subheader:

2>if more than one LCG has data available for transmission in the TTIwhere the BSR is transmitted: report Truncated BSR of the LCG with thehighest priority logical channel with data available for transmission;

2>else report Short BSR.

1>else if the number of padding bits is equal to or larger than the sizeof the Long BSR plus its subheader, report Long BSR.

If the BSR procedure determines that at least one BSR has been triggeredand not cancelled:

1>if the MAC entity has UL resources allocated for new transmission forthis TTI:

2>instruct the Multiplexing and Assembly procedure to generate the BSRMAC CE(s);

2>start or restart periodicBSR-Timer except when all the generated BSRsare Truncated BSRs;

2>start or restart retxBSR-Timer.

1>else if a Regular BSR has been triggered andlogicalChannelSR-ProhibitTimer is not running:

2>if an uplink grant is not configured or the Regular BSR was nottriggered due to data becoming available for transmission for a logicalchannel for which logical channel SR masking (logicalChannelSR-Mask) issetup by upper layers:

3>a scheduling request shall be triggered.

2>else if the Regular BSR was triggered due to data becoming availablefor transmission for a logical channel for relay purpose; or if theRegular BSR was triggered due to data becoming available fortransmission from the group of which priority was changed to higherpriority e.g. emergency situation.

3>a scheduling request shall be triggered.

A MAC PDU shall contain at most one MAC BSR CE, even when multipleevents trigger a BSR by the time a BSR can be transmitted in which casethe Regular BSR and the Periodic BSR shall have precedence over thepadding BSR. The MAC entity shall restart retxBSR-Timer upon indicationof a grant for transmission of new data on any UL-SCH.

All triggered BSRs shall be cancelled in case the UL grant(s) in thissubframe can accommodate all pending data available for transmission butis not sufficient to additionally accommodate the BSR MAC CE plus itssubheader. All triggered BSRs except BSRs reflecting relayed data shallbe cancelled when a BSR not reflecting relayed data is included in a MACPDU for transmission. All triggered BSRs reflecting relayed data fromthe ProSe Source shall be cancelled when a BSR reflecting relayed datafrom the ProSe Source is included in a MAC PDU for transmission.Alternatively, all triggered BSRs reflecting relayed data for the ProSeDestination shall be cancelled when a BSR reflecting relayed data forthe ProSe Destination is included in a MAC PDU for transmission.Alternatively, all triggered BSRs reflecting relayed data from the ProSeSource for the ProSe Destination shall be cancelled when a BSRreflecting relayed data from the ProSe Source for the ProSe Destinationis included in a MAC PDU for transmission.

The MAC entity shall transmit at most one Regular/Periodic BSR in a TTI.If the MAC entity is requested to transmit multiple MAC PDUs in a TTI,it may include a padding BSR in any of the MAC PDUs which do not containa Regular/Periodic BSR.

All BSRs transmitted in a TTI always reflect the buffer status after allMAC PDUs have been built for this TTI. Each LCG shall report at the mostone buffer status value per TTI and this value shall be reported in allBSRs reporting buffer status for this LCG. A Padding BSR is not allowedto cancel a triggered Regular/Periodic BSR. A Padding BSR is triggeredfor a specific MAC PDU only and the trigger is cancelled when this MACPDU has been built.

BSR MAC CEs consist of either:

short BSR and truncated BSR format: one LCG ID field and onecorresponding buffer size field; or

long BSR format: four buffer size fields, corresponding to LCG IDs #0through #3.

FIG. 13 shows an example of short BSR and truncated BSR MAC CE. FIG. 14shows an example of long BSR MAC CE.

The BSR formats are identified by MAC PDU subheaders with LCIDs.

The fields LCG ID and buffer size are defined as follow:

LCG ID: The LCG ID field identifies the group of logical channel(s)which buffer status is being reported. The length of the field is 2bits. A specific LCG ID is dedicated to reflect buffer status forrelaying data in the group of logical channel(s) to eNB.

Buffer size: The buffer size field identifies the total amount of dataavailable across all logical channels of a logical channel group afterall MAC PDUs for the TTI have been built. The amount of data isindicated in number of bytes. It shall include all data that isavailable for transmission not only in the transmitting RLC layer and inthe transmitting PDCP layer over Uu but also in the receiving RLC layerand the receiving PDCP layer over PC5. The size of the RLC and MACheaders are not considered in the buffer size computation. The length ofthis field is 6 bits.

When the SL BSR is used to reflect the user data to be relayed, the SLBSR procedure may be performed as follows. The SL BSR procedure is usedto provide the serving eNB with information about the amount of sidelinkdata available for sidelink transmission in the SL buffers of the MACentity as well as the amount of data available for uplink transmissionin the UL buffers of the MAC entity for relaying data from another UE tothe serving eNB. RRC controls BSR reporting for the sidelink byconfiguring the two timers periodic-BSR-TimerSL and retx-BSR-TimerSL.Each sidelink logical channel is allocated to an LCG with LCGID set to“11” and belongs to a ProSe destination.

A SL BSR shall be triggered if any of the following events occur:

1>if the MAC entity has a configured SL-RNTI:

2>SL data, for a sidelink logical channel of a ProSe destination,becomes available for transmission in the RLC entity or in the PDCPentity and there is currently no data available for transmission for anyof the sidelink logical channels belonging to the same ProSedestination, in which case the SL BSR is referred below to as “RegularSL BSR”;

2>UL resources are allocated and number of padding bits remaining aftera Padding BSR has been triggered is equal to or larger than the size ofthe Sidelink BSR MAC CE containing the buffer status for at least oneProSe destination plus its subheader, in which case the SL BSR isreferred below to as “Padding SL BSR”;

2>retx-BSR-TimerSL expires and the MAC entity has data available fortransmission for any of the sidelink logical channels, in which case theSL BSR is referred below to as “Regular SL BSR”;

2>periodic-BSR-TimerSL expires, in which case the SL BSR is referredbelow to as “Periodic SL BSR”;

1>else if the MAC entity is configured for relay:

2>UL data, for a logical channel which belongs to a LCG, becomesavailable for relay transmission in the transmitting RLC entity over Uuor in the transmitting PDCP entity over Uu and either the data belongsto a logical channel with higher priority than the priorities of thelogical channels which belong to any LCG and for which data is alreadyavailable for transmission, or there is no data available fortransmission for any of the logical channels which belong to a LCG, inwhich case the BSR is referred below to as “Regular BSR”;

1>else:

2>An SL-RNTI is configured by upper layers and SL data is available fortransmission in the RLC entity or in the PDCP entity, in which case theSidelink BSR is referred below to as “Regular SL BSR”.

For Regular and Periodic SL BSR:

1>if the number of bits in the UL grant is equal to or larger than thesize of a SL BSR containing buffer status for all ProSe Destinationshaving data available for transmission plus its subheader:

2>report SL BSR containing buffer status for all ProSe Destinationshaving data available for transmission;

1>else report Truncated SL BSR containing buffer status for as manyProSe Destinations having data available for transmission as possible,taking the number of bits in the UL grant into consideration.

For Padding SL BSR:

1>if the number of padding bits remaining after a Padding BSR has beentriggered is equal to or larger than the size of a SL BSR containingbuffer status for all ProSe Destinations having data available fortransmission plus its subheader:

2>report SL BSR containing buffer status for all ProSe Destinationshaving data available for transmission;

1>else report Truncated SL BSR containing buffer status for as manyProSe Destinations having data available for transmission as possible,taking the number of bits in the UL grant into consideration.

If the BSR procedure determines that at least one SL BSR has beentriggered and not cancelled:

1>if the MAC entity has UL resources allocated for new transmission forthis TTI and the allocated UL resources can accommodate a SL BSR MAC CEplus its subheader as a result of logical channel prioritization:

2>instruct the Multiplexing and Assembly procedure to generate the SLBSR MAC CE(s);

2>start or restart periodic-BSR-TimerSL except when all the generated SLBSRs are Truncated SL BSRs;

2>start or restart retx-BSR-TimerSL;

1>else if a Regular SL BSR has been triggered:

2>if an UL grant is not configured:

3>a scheduling request shall be triggered.

A MAC PDU shall contain at most one SL BSR MAC CE, even when multipleevents trigger a SL BSR by the time a SL BSR can be transmitted in whichcase the Regular SL BSR and the Periodic SL BSR shall have precedenceover the padding SL BSR. The MAC entity shall restart retx-BSR-TimerSLupon reception of an SL grant.

All triggered SL BSRs except SL BSRs reflecting relayed data shall becancelled in case the remaining SL grant(s) valid for this SC period canaccommodate all pending data available for transmission. All triggeredSL BSRs except SL BSRs reflecting relayed data shall be cancelled when aSL BSR not reflecting relayed data (except for Truncated SL BSR) isincluded in a MAC PDU for transmission. All triggered SL BSRs shall becancelled, and retx-BSR-TimerSL and periodic-BSR-TimerSL shall bestopped, when upper layers configure autonomous resource selection. Alltriggered SL BSRs reflecting relayed data from the ProSe Source shall becancelled when a SL BSR reflecting relayed data from the ProSe Source isincluded in a MAC PDU for transmission. Alternatively, all triggered SLBSRs reflecting relayed data for the ProSe Destination shall becancelled when a SL BSR reflecting relayed data for the ProSeDestination is included in a MAC PDU for transmission. Alternatively,all triggered SL BSRs reflecting relayed data from the ProSe Source forthe ProSe Destination shall be cancelled when a SL BSR reflectingrelayed data from the ProSe Source for the ProSe Destination is includedin a MAC PDU for transmission.

The MAC entity shall transmit at most one Regular/Periodic SL BSR in aTTI. If the MAC entity is requested to transmit multiple MAC PDUs in aTTI, it may include a padding SL BSR in any of the MAC PDUs which do notcontain a Regular/Periodic SL BSR.

All SL BSRs transmitted in a TTI always reflect the buffer status afterall MAC PDUs have been built for this TTI. Each ProSe Destination shallreport at the most one buffer status value per TTI and this value shallbe reported in all SL BSRs reporting buffer status for this ProSeDestination. A Padding SL BSR is not allowed to cancel a triggeredRegular/Periodic SL BSR. A Padding SL BSR is triggered for a specificMAC PDU only and the trigger is cancelled when this MAC PDU has beenbuilt.

SL BSR MAC CE consists of SL BSR and truncated SL BSR, which includesone group index field, one LCG ID field and one corresponding buffersize field per reported target group.

FIG. 15 shows an example of SL BSR MAC CE for even N. FIG. 16 shows anexample of SL BSR MAC CE for odd N.

The SL BSR is identified by MAC PDU subheaders with LCID.

For each included group, the fields are defined as follow:

Group index: The group index field identifies the ProSe destination. Thelength of this field is 4 bits. The value is set to the index of thedestination reported in destinationlnfoList. A specific Group index isdedicated to reflect buffer status for relaying data in the group oflogical channel(s) to eNB.)

LCG ID: The LCG ID field identifies the group of logical channel(s)which buffer status is being reported. The length of the field is 2 bitsand it is set to “11”; A specific LCG ID is dedicated to reflect bufferstatus for relaying data in the group of logical channel(s) to eNB.

Buffer Size: The buffer size field identifies the total amount of dataavailable across all logical channels of a ProSe destination after allMAC PDUs for the TTI have been built. The amount of data is indicated innumber of bytes. It shall include all data that is available fortransmission not only in the transmitting RLC layer and in thetransmitting PDCP layer over Uu but also in the receiving RLC layer andthe receiving PDCP layer over PCS. The size of the RLC and MAC headersare not considered in the buffer size computation. The length of thisfield is 6 bits.

R: Reserved bit, set to “0”.

FIG. 17 shows a method for performing, by a relay UE, a BSR procedureaccording to an embodiment of the present invention.

In step S200, the relay UE receives data to be relayed from a remote UEvia sidelink Before receiving the data to be relayed, the relay UE maytransmit a relay request to the network. Further, the relay UE mayreceive a relay configuration, which configures a data radio bearer usedto relay data only, from the network.

In step S210, the relay UE triggers a BSR or a sidelink BSR for the datato be relayed. The BSR or the sidelink BSR informs the network aboutamount of data available for UL transmission of the data to be relayed.The BSR or the SL BSR may include a specific LCG dedicated to relaying.A buffer size field in the BSR or the SL BSR may include UL data in atransmitting L2 entity over Uu interface and sidelink data in areceiving L2 entity over PC5 interface. In this case, the BSR may betriggered by data available in the receiving L2 entity over PC5interface, and the SL BSR is triggered by the data available in thetransmitting L2 entity over Uu interface.

The triggered BSR or the triggered sidelink BSR may be canceled when theBSR or the sidelink BSR is included in a MAC PDU. The BSR may beprioritized over other BSRs in a LCP procedure when the data for a groupof which priority is changed due to emergency situation. The SL BSR maybe prioritized over other sidelink BSRs in a LCP procedure when the datafor a group of which priority is changed due to emergency situation. TheSL BSR may be prioritized over BSRs and other sidelink BSRs in a LCPprocedure when the data for a group of which priority is changed due toemergency situation.

In step S220, the relay UE transmits the BSR or the sidelink BSR to anetwork. After transmitting the BSR or the sidelink BSR, the relay UEmay receive a relay grant from the network. The relay UE may transmitthe data to be relayed to the network.

FIG. 18 shows a wireless communication system to implement an embodimentof the present invention.

A relay UE 800 includes a processor 810, a memory 820 and a transceiver830. The processor 810 is configured to implement proposed functions,procedures and/or methods described in this description. That is,according to the description above, the processor 810 is configured totrigger BSR or SL BSR which is used to inform the serving eNB about theamount of data available for uplink transmission of relayed data. Layersof the radio interface protocol may be implemented in the processor 810.The memory 820 is operatively coupled with the processor 810 and storesa variety of information to operate the processor 810. The transceiver830 is operatively coupled with the processor 810, and transmits and/orreceives a radio signal. The transceiver 830 receives data to be relayedfrom a remote UE, and transmits the triggered BSR or SL/BSR to anetwork. The transceiver 830 transmits the data to be relayed to thenetwork.

A remote UE or eNB 900 includes a processor 910, a memory 920 and atransceiver 930. The processor 910 is configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 910. The memory 920 is operatively coupled with the processor910 and stores a variety of information to operate the processor 910.The transceiver 930 is operatively coupled with the processor 910, andtransmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The transceivers 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

1. A method for performing, by a relay user equipment (UE), a bufferstatus reporting (BSR) procedure in a wireless communication system, themethod comprising: receiving data to be relayed from a remote UE viasidelink; trigger a BSR or a sidelink BSR for the data to be relayed;and transmit the BSR or the sidelink BSR to a network.
 2. The method ofclaim 1, wherein the BSR or the sidelink BSR informs the network aboutamount of data available for uplink (UL) transmission of the data to berelayed.
 3. The method of claim 1, wherein the BSR or the SL BSRincludes a specific logical channel group (LCG) dedicated to relaying.4. The method of claim 1, wherein a buffer size field in the BSR or theSL BSR includes UL data in a transmitting L2 entity over Uu interfaceand sidelink data in a receiving L2 entity over PC5 interface.
 5. Themethod of claim 4, wherein the BSR is triggered by data available in thereceiving L2 entity over PC5 interface.
 6. The method of claim 4,wherein the SL BSR is triggered by the data available in thetransmitting L2 entity over Uu interface.
 7. The method of claim 1,wherein the triggered BSR or the triggered sidelink BSR is canceled whenthe BSR or the sidelink BSR is included in a media access control (MAC)protocol data unit (PDU).
 8. The method of claim 1, wherein the BSR isprioritized over other BSRs in a logical channel prioritization (LCP)procedure when the data for a group of which priority is changed due toemergency situation.
 9. The method of claim 1, wherein the SL BSR isprioritized over other sidelink BSRs in a LCP procedure when the datafor a group of which priority is changed due to emergency situation. 10.The method of claim 1, wherein the SL BSR is prioritized over BSRs andother sidelink BSRs in a LCP procedure when the data for a group ofwhich priority is changed due to emergency situation.
 11. The method ofclaim 1, further comprising transmitting a relay request to the network.12. The method of claim 1, further comprising receiving a relayconfiguration, which configures a data radio bearer used to relay dataonly, from the network.
 13. The method of claim 1, further comprisingreceiving a relay grant from the network.
 14. The method of claim 13,further comprising transmitting the data to be relayed to the network.15. A relay user equipment (UE) in a wireless communication system, therelay UE comprising: a memory; a transceiver; and a processor coupled tothe memory and the transceiver, wherein the processor is configured to:control the transceiver to receive data to be relayed from a remote UEvia sidelink, trigger a buffer status reporting (BSR) or a sidelink BSRfor the data to be relayed, and control the transceiver to transmit theBSR or the sidelink BSR to a network.